1. Field of the Invention
The present invention relates to a hand-held eye-refractometer for objectively measuring the refracting power of an eye to be examined.
2. Related Background Art
Some eye-refractometers have a fogging function. Normally, when a target is presented to an eye to be examined, the function of the human eye called accommodation acts to fix itself on the target. For this reason, in order to measure an accurate refracting power, the accommodation function which acts to fix the eye on the target must be removed from the eye to be examined. In order to remove or relax the accommodation function that acts to fix the eye to be examined on the target, a fogging mechanism for moving the target is arranged.
In order to measure an accurate refracting power, the fogging operation for moving the target must be basically performed prior to obtention of the eye refracting power measurement data. For this reason, in a conventional eye-refractometer, a fogging operation is automatically started upon depression of a measurement switch, and thereafter, eye refracting power measurement data is obtained.
In the conventional eye-refractometer, upon depression of the measurement switch, a predetermined number of measurement data are obtained, and the plurality of data are subjected to statistical processing such as averaging processing. Thereafter, the statistical processing result is displayed.
The eye-refractometer is often used for eyes to be examined, which are impossible or hard to measure, i.e., the eyes of 0- to 3-year old babies, the eyes of patients under operation represented by that of cataract, the eyes of patients suffering from diseases such as nystagmus, the eyes of animals, and the like as objects to be measured. For most of these eyes to be examined, it is impossible or hard to expect fixation of gaze. Therefore, the operation of the fogging mechanism is often of no use, and the conventional eye-refractometer, which automatically starts a fogging operation upon depression of the measurement switch, vainly prolongs the measurement-time. Furthermore, as for the above-mentioned eyes to be examined, it is important for a measurement operator to obtain data. However, in the conventional eye-refractometer, a measurement operator can obtain a measurement value after the eye-refractometer itself obtains a predetermined number of data and performs statistical processing of these data. For example, when the eye-refractometer itself is hard to obtain a predetermined number of measurement data owing to the nature of a specific eye to be examined, a long period of time is required until a measurement value is obtained. In the worst case, the measurement operator cannot obtain a measurement value.